This invention relates to an oil pump for a four cycle outboard motor and more particularly to an improved driving arrangement for such an oil pump.
Although two cycle internal combustion engines have been the accepted powerplant for use in outboard motors for a long time, environmental conditions are dictating the use of four cycle engines. This presents some significant problems to the designer because of the more complicated nature of a four cycle engine when compared to a two cycle engine. One of the particular complicating factors with applying four cycle engines to outboard motors is the lubrication system for such engines.
Although the use of recirculating of lubrication systems provide much better environmental control than is possible with two cycle engines, there are significant problems with adapting conventional automotive type lubricating systems to outboard motor applications. One reason for this is the fact that the outboard motor crankshaft or engine output shaft rotates about a vertical rather than a horizontal axis. Thus, the crankcase chamber is not practical to be utilized as an oil reservoir for the engine.
Therefore, it has been the practice to provide an oil reservoir for the engine in the area below the engine and generally in the otherwise void area formed at the upper end of the driveshaft housing. This means, however, that the oil must be pumped from this reservoir to the engine lubricating system by an oil pump. The drive and location of these pumps is quite important. That is, the pump should be located in a manner that is driven easily off the engine and yet so that it is positioned in proximity to the oil pan or oil reservoir so as to minimize the length of flow paths, particularly on the inlet side of the pump.
Although one form of arrangement for driving the oil pump for a four cycle engine in an outboard motor has employed driving of the oil pump off of an overhead cam shaft of the engine, there are some potential disadvantages with this type of arrangement. Specifically, the cam shafts are driven at one-half crankshaft speed and hence, the oil pump will be driven slower than the crankshaft. This may not always provide the requisite amounts of lubricant for some types of engines.
There has been proposed, therefore, an arrangement for driving the oil pump from the engine output shaft at the interface where it joins the driveshaft for the propulsion unit. Several embodiments of such arrangements are shown in the copending application entitled "Oil Pump for Outboard Motor", Ser. No. 08/996,529 filed Dec. 23, 1997 in the name of Hitoshi Watanabe et al., which application is assigned to the assignee hereof.
With the arrangement shown in this copending patent application, the oil pump is driven off of the engine crankshaft at the area where it is joined to the driveshaft. This permits the oil pump to be positioned in close proximity to the underlying oil pan and greatly simplifies the construction. In addition, the oil inlet and outlet passages can be positioned free of the driving and driven components and thus permit a more leak-free environment.
One embodiment of that application utilizes the splined connection between the driveshaft and the engine output shaft as the driving arrangement for the oil pump. Although this has significant advantages, the construction shown in that application may present some problems in certain types of operations.
This may be understood best by reference to FIGS. 1-3 of this application which illustrate generally the arrangement shown in the embodiment of FIG. 16 of that application. This construction will now be described by reference to these figures which are basically cross-sectional views taken through the area at the upper portion of the driveshaft housing and the lower unit and the lower portion of the power head. As described below, FIG. 1 is a cross-sectional view taken through the oil pump in this area while FIG. 2 is an enlarged view of the area shown in FIG. 1 and FIG. 3 is a further enlarged view of the area encompassed by the circle 3 in FIG. 2.
As seen in these figures, the engine crankshaft 21 has a portion that protrudes below a lower face of the engine cylinder block, crankcase assembly 22. This portion of the crankshaft 21 is provided with a splined opening 23. A splined end 24 of a driveshaft 25 is received in and thus drivingly coupled to the engine crankshaft 21. The driveshaft 25 depends into the driveshaft housing and lower unit of the outboard motor for driving its propulsion device.
It should be seen that the splined portion 24 of the driveshaft 25 is substantially longer than the length of the crankshaft splines 23. This permits driving engagement with a pump driving element 26 of a gerotor type oil pump, indicated generally by the reference numeral 27 and mounted on top of a supporting plate 28 formed at the upper end of the driveshaft housing. This pump driving member 26 has a splined inner portion 29 so as to provide a driving relationship therewith. The outer portion of the driving member 26 drives the inner gear 31 of the gerotor type pump 27 which cooperates with a fixed outer gear 32 to provide the pumping action in a manner well known in the art.
As may be best seen in FIGS. 2 and 3, the arrangement is such that there must be a small clearance area z between the lower end of the crankshaft 21 and the upper end of the inner portion of the pump driving member 31. Thus, the splined portion 24 of the driveshaft 25 has a first part 33 which is engaged with the crankshaft splines 23 and a second part 34 that is engaged with the inner splines of the pump drive member 31 these being the splines 29. The driveshaft 24 is obviously subjected to varying and at times substantial torsional forces. This means that there will be stress raised areas WI and W2 at the ends of the splined connections between the crankshaft 21 and the pump driving member 31. Thus, there is a risk that a fracture or failure may occur in this area. Of course, this can be offset by making the diameters larger and the pieces larger, but this is obviously not desirable.
In addition to this problem, even if failure does not occur, a permanent deformation of the splines in the area z and specifically the splined portion 24 of the driveshaft 25 may become deformed and it may be difficult to disassemble the construction.
It is, therefore, a principal object of this invention to provide an improved oil pump drive arrangement suitable for use in an outboard motor.
It is a further object of this invention to provide an improved and simplified oil pump drive arrangement for an outboard motor of the type generally described and one in which stress risers and other problems associated therewith can be eliminated.